The invention herein relates to providing semiconductor devices with charge-coupled devices. More particularly, the invention relates to providing self-aligned barrier and conductive regions in conductively connected charge-coupled devices.
The introduction of charge-coupled devices (CCD's) in recent years has given promise of monolithic integrated circuits having a very high component device density for performing several signal processing functions. Both digital signal processing functions and analog signal processing functions can be performed by charge-coupled devices.
Among the various charge-coupled devices proposed to date is the conductively connected charge-coupled device (C4D) originally proposed by Krambeck, Strain, Smith and Pickar in an article entitled "Conductively Connected Charge-Coupled Device" published in the IEEE Transactions on Electron Devices, Vol. Ed-21, No. 1, January 1974. While there are some difficulties associated with the conductively connected charge-coupled devices concerning transfer efficiency, there are also several attractive features including operation with two-phase clocking without the need for overlapping electrodes in the storage and transfer regions. In these devices, each transfer region contains a barrier region under the electrodes and contains a connecting conductive region between the electrodes. The storage regions also occurs under the electrodes.
Typically, a two-phase charge-coupled device monolithic integrated circuit contains a sequence of storage and transfer regions alternating with one another in the silicon below an insulating layer supporting the component device electrodes. As indicated above, there is one region of each kind, storage or transfer, for each CCD component device and the sequence of alternating regions, or the sequence of CCD component devices, is provided in a generally linear geometrical arrangement. Often, however, a single line of such devices in the integrated circuit is insufficient in number for the signal processing function to be performed. Hence, the entire device sequence for performing a processing function is often formed by folding lines of devices back and forth one or more times in serpentine fashion to form a signal processing sequence having parallel lines of devices. Since the entire sequence is constructed in a single fabrication process, if the barrier region for a component device in a C4D integrated circuit is misaligned with the corresponding component device electrode in a first line of component devices in a signal processing sequence, the barrier region for a component device in an adjacent line of devices in the sequence will be misaligned with its component device electrode in the opposite direction.
This misalignment of barrier regions with corresponding device electrodes in one direction in alternate device lines in a processing sequence and misalignment in the opposite direction in the remaining device lines in the signal processing sequence, leads to varying transfer characteristics among the component devices by device lines throughout a sequence. This is because the component devices in alternate device lines in the signal processing sequence will have areas adjacent to the insulating layer of different sizes in the device storage regions. Thus, there will be difficulties when a packet of charge in the component device at the end of one device line, if this is a line having component devices with larger storage region areas, is transferred to the adjacent device line having component devices with smaller storage region areas. The full packet of charge from the first line is in part spilled forward when reaching the adjacent line. The result is that the original size of the charge packet in the first device line is reduced and the spilled forward charge represents false information in the second device line. Therefore, having self-aligned barrier regions with respect to corresponding component device electrodes for each component device is very desirable to avoid having storage areas of different sizes occur in the various component devices.